The invention relates to a method of reducing the aflatoxin content of an oilseed meals.
Aflatoxins B.sub.1, B.sub.2, G.sub.1, G.sub.2 are highly toxic metabolites developed by certain moulds, more particularly by Aspergillus Flavus. The latter mould grows on peanut-oil seed, cottonseed and other seeds in tropical climates having a relative humidity of more than 85 percent. Aflatoxins are very stable chemically, owing to their molecular structure. They are not affected by thermal treatment at 160.degree. C. for an hour.
Among the aforementioned aflatoxins, aflatoxin B.sub.1 is considered the most toxic and is most frequently present in cakes of oil-bearing seeds and other products liable to be infected by Aspergillus Flavus. The aflatoxin can be detoxified only by profoundly modifying the original chemical structure of the toxin. Research has shown, however, that it is not sufficient to open the lactone ring (shown in analysis by the disappearance of the fluorescent chromatographic spots characteristic of aflatoxin) since, as can be shown, the molecule can revert to its original form and become toxic again. The molecule must be destroyed by oxidizing certain parts of it (the double bonds in the ring), in which case the starting substance must be the "open lactone ring" form. Experience shows that though the ring is opened by alkalinity in general, it is oxidized only by alkalinity produced by certain strong alkalis.
Food contaminated by aflatoxins is unsuitable for consumption. The F.A.O. have fixed the total quantity of aflatoxin acceptable in animal food at 50 ppb. The abbreviation "ppb" means "parts per billion," which is equivalent to "mg/tonne". The term "billion", as used herein, means "1,000,000,000". This limit is much lower than the 200 to 1000 ppb frequently found in contaminated peanuts or peanut oil cakes. Peanut oil cakes are an important substance in fodder for animals such as cattle and poultry, and consequently much research has been done in order to find means of decontamination.
It has been proposed, for example, to use the fermentation method. Some micro-organisms are capable of metabolizing (destroying) aflatoxins, using as substrate the polysaccharides present in the oil cakes. This method has the disadvantage of requiring expensive installations and relatively long treatment. It is used in certain industrial countries such as France, where the climate is less humid and Aspergillus Flavus cannot start growing again from its spores.
It has also been proposed to use an extraction method and organic solvents. A number of organic solvents such as methanol, ethanol, acetone and chloroform can extract aflatoxin from oil cakes. This method requires expensive installations and may be dangerous, since the solvents are inflammable. It has the further disadvantage of eliminating other fatty residues in the oil cakes, thus lowering their nutritional value.
Methods of detoxication have also been proposed wherein use is made of chemical products capable of converting aflatoxins. Although many chemical agents can react with aflatoxins, use can be made of only a few, either because they are themselves toxic or because they excessively reduce the nutritional value of the products treated, or because they are too expensive.
Strong bases are the most effective. They hydrolyze the lactone in aflatoxins and form the corresponding salt of the carboxyl group and the phenolate: ##STR1##
In this form, aflatoxins slowly oxidise in air and disappear from the oil cakes in a few weeks.
In one known method (U.S. Pat. No. 3,429,709) the reagent used is ammonia. Ammonia, however, is not a sufficiently strong base; it is very volatile and cannot be used at ambient pressure and at a temperature of 80.degree.-100.degree. C. The pH of a hydrated product (20% water) is of the order of 8.5 to 9 before heating but falls to 8-8.5 during treatment at 90.degree.-100.degree. C.
It has also been proposed (U.S. Pat. No. 3,585,041) to use methylamine which is less volatile than ammonia and gives a pH which is 1 to 1.5 pH units greater than that given by the same molecular concentration of ammonia--i.e. methylamine is about 20 times as strong a base. However, it is very disadvantageous to use methylamine in the proposed proportions (0.6-1.5 percent of the weight of the contaminated product), since it is difficult to eliminate the methylamine from the product, which acquires a pungent smell and disagreeable taste which persists even after vacuum treatment or exposure to air for several weeks. Probably methylamine becomes relatively strongly fixed to the acid (--COOH) groups of the proteins.
The object of the invention is to provide a method which, though using an organic amine as the reagent, obviates the aforementioned disadvantage of the known method.